I've seen in several places that pet lifespans for the puppy/kitten and adult stages are:
Puppy/Kitten -- Adult
1.5 Days -- 12 Days -- Short
3 Days -- 24 Days -- Normal
12 Days -- 96 Days --Long
This is incorrect. They have no fixed number of days.
I tested this out with the control mod that allows you to see the ages of pets. I took 3 groups of 7 pets with a mix of 3-4 dogs/cats each. These were all newly created in CAP. I checked ages as puppies/kittens and then immediately aged them to adults in CAS/CAP to check ages again. Here's what I found:
There are definitely no set ages for pets....they all varied along a range. Also, cats have consistently longer lifespans. Here are the numbers that I saw:
Short Lifespan: 0-1 days
Normal Lifespan: 1-2 days
Long Lifespan: 4-6 days for dogs; 5-6 days for cats
Keep in mind that there are still the additional days before the auto-aging kicks in once they are ready to age up. On long, this is typically 4 extra days. So that's why puppies and kittens generally age up after around 9-10 days total on long. For short, you're looking at somewhere between 1-2 days total and on normal, you're looking at 2-3 days total.
Short Lifespan: 9-10 days for dogs; 11-12 days for cats
Normal Lifespan: 17-20 days for dogs; 21-24 days for cats
Long Lifespan: 69-79 days for dogs; 88-94 days for cats
These numbers do not include the extra day or days for auto-aging after the pet has filled their age bar. You shouldn't get more than 1 extra day on normal....but long lifespan should add 4 extra days to the above numbers before the auto-aging takes place.
As with regular sims, the number of days for elder pets varies and I didn't test them.